This invention relates to a drive device for rotary tube furnaces, mills and the like, comprising a main drive including a main motor, main gearing disposed between the main motor and the unit being driven, an auxiliary drive including an auxiliary motor, auxiliary gearing disposed between the auxiliary motor and the main gearing; a clutch between the main and auxiliary gearings and a centrifugal brake in the vicinity of the auxiliary drive.
With known drive devices of the above type, the auxiliary drive is disconnected by means of the clutch during normal operation. If now the main drive is switched off or the main motor fails for any reason, the rotary tube furnace swings back into a position determined by the centre of gravity. The excessive rotary speeds which can occur in such cases may lead to serious damage to the main gearing and main motor.
To avoid these disadvantages a drive device has already been developed (German Gebrauchsmuster 71 30 651) wherein an overriding clutch is provided for overriding the auxiliary drive. If the rotary furnace swings backward, this clutch brings into operation a centrifugal brake disposed in or at the auxiliary gearing, so that the entire drive is protected from excessively fast rotation. This centrifugal brake provided in the auxiliary drive also becomes operative if the auxiliary motor fails (when the rotary furnace is being driven by the auxiliary drive) and the rotary furnace for that reason swings backward.
However, it now has been found that in many cases (especially for rotary furnaces with planetary coolers) in certain circumstances such as during repairs, the rotary furnace can swing forward in the direction of operational rotation when the motor is switched off. In such a case the overriding clutch in the known drive device referred to above would release the rotary furnace to swing in the operational rotation direction, which may involve dangerously excessive speeds.